[ncl-talk] index lists in assignment

[Dennis Shea]

My recollection is that the way fortran and NCL handled 'indirect
subscripting' (my words) yielded different results.
Hence, the 'expected results' are colored by past expeerience in fortran.

Unfortunately, I can not find my NCL/fortran   example. Sorry.

D


On Fri, Nov 30, 2018 at 11:27 AM Rick Brownrigg <brownrig at ucar.edu> wrote:

> Hi Axel,
>
> Apologies in delay in getting back to you on this.  As far as I can tell,
> the behavior ox "x(idx) = x(idx) + z" is the intended behavior (perhaps not
> the same as "desired" behavior in your case), in the sense that the
> right-hand side is completely evaluated before the (re)assignment to the
> variable "x": is performed.
>
> The do-loop approach does work -- it it just unbearably slow?  Without
> knowing more about your data, I don't have a suggestion for how to avoid
> looping.
>
> Rick
>
>
> On Thu, Nov 29, 2018 at 10:37 AM Axel Seifert <Axel.Seifert at dwd.de> wrote:
>
>>
>> Maybe I should add that the output of my little script is
>>
>>
>> (0)      0 0
>> (1)      3 4
>> (2)      2 2
>>
>>
>> This is with NCAR Command Language Version 6.3.0
>>
>>
>> The variables x and y are
>>
>>
>> Variable: x
>> Type: float
>> Total Size: 12 bytes
>>             3 values
>> Number of Dimensions: 1
>> Dimensions and sizes:   [3]
>> Coordinates:
>> Number Of Attributes: 1
>>   _FillValue :  9.96921e+36
>> (0)      0
>> (1)      3
>> (2)      2
>>
>> Variable: y
>> Type: float
>> Total Size: 12 bytes
>>             3 values
>> Number of Dimensions: 1
>> Dimensions and sizes:   [3]
>> Coordinates:
>> Number Of Attributes: 1
>>   _FillValue :  9.96921e+36
>> (0)      0
>> (1)      4
>> (2)      2
>>
>>
>>
>> Am 24.11.2018 um 15:16 schrieb Seifert Axel:
>>
>>
>> Hi,
>>
>>
>> I have a somewhat unexpected behavior when using index lists. Here a
>> simplified example:
>>
>>   x = new( 3, float)
>>   x = 0.0
>>   y = x
>>
>>   z = (/1.,2.,3./)
>>   idx = (/1,2,1/)
>>
>>   x(idx) = x(idx) + z
>>
>>   do i=0,dimsizes(idx)-1
>>     y(idx(i)) = y(idx(i)) + z(i)
>>   end do
>>
>>   print(" "+x+" "+y)
>>
>> I would have expected that x and y end up being the same, but they are
>> not. The double assignment to index 1 does not work for the vector
>> assignment. Is this the intended behavior for arrays in ncl?
>>
>> How can I get the 2nd behavior and still avoid the do-loop?
>>
>> In my case I am assigning measured values from satellite overpasses to a
>> global grid and it can of course happen that I have multiple overpasses for
>> a grid point in an observation vector. Hence, in addition to the sum of the
>> values I would count the number of overpasses
>>
>>   cnt = (/0,0,0/)
>>   cnt(idx) = cnt(idx) + 1
>>   print(" "+cnt)
>>
>> and then xavg = x/cnt should give me the proper average for, for example,
>> one hour of data. What I need in the end is the correct average for xavg
>> and the number of measurements used at each grid point.
>>
>> Thanks in advance for any helpful comments and suggestions.
>>
>> Axel
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> ncl-talk mailing listncl-talk at ucar.edu
>> List instructions, subscriber options, unsubscribe:http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>
>>
>> _______________________________________________
>> ncl-talk mailing list
>> ncl-talk at ucar.edu
>> List instructions, subscriber options, unsubscribe:
>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>
> _______________________________________________
> ncl-talk mailing list
> ncl-talk at ucar.edu
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.ucar.edu/pipermail/ncl-talk/attachments/20181130/6262459e/attachment.html>